Epoxidation of unsatukated compounds



EPOXIDATION on UNsArtJnArED COMPOUNDS 7 Benjamin Phillips and Paul S.Starcher, 'Charlestomnnd Donald L. MacPeek, South Charleston, W. Va.,as-

"signors to Union Carbide Corporation, a corporation of New York NoDrawing. Application November 13,1957 I SerialNo. 696,044}; t 14 Claims;ca. 260- -348.'5)

of said olefinic' esters are satisfied by at least two hydrocarbongroups, to produce, the corresponding vinyl and allyl glycidic esters. v

The synthesis of certain types of 2,3.-epo1 yesters is well known in theart. In 1892, Erlenmeyer produced ethyl /3-p henyl-a, 8-epoxypropionateby the interaction I of benzaldehyde and ethyl chloroacetate in thepresence of sodium. Between '1904 and 1932 Erlenmeyer.s work wasexpanded by Darzens who generally favored the,

United BratcsfPfi acid with the corresponding alpha,bet a'-olefinicester 'of vinyl orallyl alcohol, wherein the valences, collectively,

of the alphaand beta carbon atoms of the carboxylic acid residue, i.e.,

y h m phabctalefinic ester position, i.e.,

V wherein the valences, collectively, of the alpha and use of sodiumethoxid'e as the condensing agent. A

modification by Darzens of his general procedure wat the reaction ofketones oraldehydes with ethyl .dichloroacetate and dilutemagnesiimramalgam, followed 'by hydrolysis of the product" to producefl-hydroxyachloroester. Treatmentrwith sodium ethoxide provided theglycidic esters. -Among the disadvantagesof the Darzens process areincluded small yields, undesirable side reactions, wide boiling range,e.g., 5 to 10 (2., of many reported glycidic esters indicatingth'epresence of impurities such as isomeric carbon or oxygen-alkylationproducts, recommended use of an inert atmosphere, in the light ofthe-instant Specification v In order to facilitate the understanding ofthe instant inventionthe alphzubeta-olefinic ester employed as re-.

economic barriers presented by the high cost of starting materials, andothers. a V r V A similar reaction with methyl sorbate and perbenzoic'acidin" chloroform over a period of from about 5 'to 10 days gave onlymethyl 4,5-epoxy-2-hexenoate and not the 2,3-ep'oxy or glycidic type ofester. Another method reported in the literature involvedthe reaction ofmethyl crotonate and perbenzoic acid to prepare methyl2.,3-epoxybutyrate. A yieldof 44 percent was obtained by a procedureinvolving a reaction period ofseveral months at 8 C. in theabsence oflight. A most recent work reported the epoxidation of acrylate, a-methylacry-lateand crotonate esters by the use of the prohibitively; expensiveperoxytrifiuoroacetic acid in a system buffered. with disodium hydrogenphosphate. Almost universally a solvent suchas methylene chloride orethylene dichloride was requiredto minimize olefin polymerization. I i iThework of'severalinvestigators was summarized by Swern (Chem. Rev., 45,50-51) in 1949 with'respect to the epoxidation of alpha,beta-unsaturatedesters with perbenzoic acid. His conclusions stated that the reactionof-perbenzoic acid with an olefin bearing a carbonyl or carboalkoxy(COOR) group in close proximityto beta carbon atoms of said carboxylicacid residue are satisfied by at least two hydrocarbon groups; whereinthe alcohol residue of said ester can be considered to be derived fromvinyl or allyl alcohol; and wherein the ester molecule, is composed ofcarbon, hydrogen and oxygen atoms, said oxygen atoms being present inester linkage only, i.e.,

|| I -o-o' For, brevity, the, term falphabeta-elefinic ester oi vinyl orallyl alcoho oftentimes will be hereinafter referred to as analpha,beta-olefinic ester. 1

Accordingly, one or more of the following objects will be achieved bythepractice "of. this invention.

It is an object of this invention to provide a novel process forpreparing vinyl and allyl glycidic esters by the-selectivemonoepoxidationof the corresponding organic alpha,beta-olefinic' esterofvinyl or allyl alcohol, said. alphabeta-olefinic ester containing atleast two bydrocarbon groups attached to the carboxylic acid residue ofthe ester. It is another object of this invention to providela novelmonoepoxidation process wherein complicatingand undesirable sidereactions are Other objects. will become apparent t'othose skilled inthe art' agent in the instant selective monoepoxidation process ischaracterized by the following general formula:

F and wherein each R, individually, can be a hydrogen atom the ethylenicbond was either slowed down to an exaggerated degree or prohibitedby thepresence of that group. The presentinyention contemplates thepreparation of vinyl or allyl glycidic esters by the reaction ofperacetic a,fl-dimethyl-fl-propylacrylate, vinyl a-ethyl-p-propyl-por ahydrocarbon group except that two, of the three variables designated asR are always hydrocarbon groups, for example, alkyl, aryl, aralkyl,alkaryl, and cycloalkyl groups.

include, among othersflnethyl, ethyl, propyl, isopropyl, butyl, amyl,isoamyl, hexyl, 2-ethylhexyl, octyl, 3,5- dimethyloctyl, decyl, dodecyl,octadecyl, cyclopentyl, cyclohexyl, phenyl, tolyl, butylphenyl, benzyl,phenethyl, phenylpropyl, and the like.

-Typica1 v B-olefinic ester compounds conforminglto structural Formula Isupra which can'be selectively monepoxidized to the corresponding vinylor allyl glycidic esters by the practice of this invention include,among others'vinyl, a-methylcrotonate, allyl a-methylcrotonate,

oz propylcrotonate, allyl a butylcrotonate, vinyl 04,-ethyl-fl-propylacrylate, allyl q-ethyl-fi -amylacrylate, vinyl In apreferred aspect two or more of the R; variables are alkyl groups.Exemplary radicals forR butylacrylate, allyl fl-ethyl-fi-hexylacrylate,allyl a-phenylcrotonate, vinyl fi-phenethyl-B-ethylacrylate, allylabenzyl-B-propylacrylate, vinyl u-tolyl-fi-butylacrylate, vinyla-cyclohexylcrotonate, allyl u-cyclopentyl-fi-ethylacrylate, and thelike. i

The monoepoxide compounds, i.e., vinyl and allyl glycidic esters,resulting from the epoxidation are characterized by the followingstructural formula:

II R R l I g tion reaction does not appear to be critical. The mono-tepoxidation of the a,B-olefinic ester reagents conforming to Formula Iabove is highly selective, and consequently, oxirane oxygen isintroduced at the site of the carbon to carbon double bond of thecarboxylic acid residue, i.e.,

to form the corresponding monoepoxidized product, i.e., vinyl or allylglycidic ester. Theoretically, however, in the epoxidation of thea,fiolefinic ester with peracetic acid, two mols of said acid can reactwith one mol of said ester to form the corresponding diepoxide product.Hence, the reaction period should be conducted fora period of timesuflicient to consume up to one mol of peraceticacid per mol of;esterreagent. The amount of peracetic acid consumed during the reaction canbe readily determined by running an analysis on samples of the reactionmixture at various intervals to ascertain'the quantity of unreactedperacetic acid therein. 'From this determination the amount of peraceticacid consumed can be simply calculated. In general, the concentration ofperacetic acid employed can vary from about 0.2 mol, and lower, to aboutmols, and higher, per mol of 0:,[3-0l6fi11iC ester reagent. The upperlimit regarding the quantity of peracetic acid .used is governed mainlyby economic and product recovery considerations. In a preferred aspect,from about 0.2 to about 2.0 mols of peracetic acid per mol ofu,fi-olefinic ester reagent can be employed, and the reaction period isconducted for a period of time sufficient to consume up to one mol ofperacetic acid per mol of peracetic acid per mol of 0t,/3- olefinicester, i.e., the reaction period is conducted for a period of timesufiicien-t to introduce oxirane oxygen at the site of the carbon tocarbon double bond of the carboxylic acid residue of the ester reagent,thus selectively producing the monoepoxidized product, vinyl or allylglycidic ester.

The epoxidation reaction can be conducted at a temperature in the rangeof from about 0 to -100 C., and preferably from about 25 to about 90 C.As a practical matter, the choice of the particular temperatureat whichto effect the monoepoxidation reaction depends, toan extent, on thenature of the alpha,beta-olefinic ester reagent. The reaction issomewhat exothermic and coolmg means, such as a water jacketencompassing there- 2,927,9 1 r r J 4 action vessel, can be provided toprevent any possible runaway temperatures.

As stated previously the reaction is conducted for a' period of timesufficient to consume up to one mol of peracetic acid per mol ofa,}9-olefinic ester employed. Periodical analysis of samples of thereaction mixture to determine the quantity of peracetic acid consumedduring the epoxidation reaction can be readily performed by theoperator. For example, the operator can intermittently remove a smallsample of the reaction mixture and add it, dropwise, to 50 cc. of aceticacid containing 10 cc. of saturated aqueous potassium iodide. Theresulting solution will be darkly colored due to the release of iodine.Subsequently, this colored mixture is titrated with 0.1 N of sodiumthiosulfate until the mixture be comes colorless. This titration is ameasure of the unreacted peracetic acid from which the amount ofperacetic acid consumed is readily. determined. In general, the reactionperiod willvary depending on the concentration of the reactants, theparticular a,;8-olefinic ester employed, the temperature, the typeanddegree of agitation of the reaction mixture, and other factors.According to the correlation of the above-illustrated factors thereaction period which is necessary to effect the consumption of up toone mol of peracetic acid per mol of a, 8-olefinic ester, i.e.,introduce oxirane oxygen at the site of the carbon to carbon double bondof the carboxylic acid residue of said ester, can be as short as minutesin length orit can be as long as 12 hours or more, e.g., from'about 30minutes to about 18 hours. 7 a

It is desirable to conduct the epoxidation reaction with equipment whichwill not foster the polymerization of the a,B-0lefinic ester or catalyzethe decomposition of peracetic acid. Equipment constructed of glass,stainless steel, aluminum and the like has been shown to be adequate forthis purpose. If desired, apolymerization inhibitor or retarder such ashydroquinone, 2,4-dinitrophenol, 2,4-dinitro-m-cresol, and the like canbe incorporated into the reaction mixture in an amount sufiicient toprevent possible polymerization of the a,;3-olefinic ester reagent.-Provision can be made for heating and/ or cooling the reactor contents.A suitable reflux-type condenser can be attached as an integral part ofthe equipment.

The particular manner of adding the reagents, i.e., the a,,B-olefinicester and peracetic acid, to the reaction vessel is not narrowlycritical. One desirable procedure is to charge the 0:,[3-Ol6fi11i0 esterto the reaction vessel and subsequently heat said ester to apredetermined temperature. At this temperature, and generally underconstant agitation, peracetic acid, preferably in an inert medium suchas ethyl acetate, acetone, and the like, is fed to the reaction vessel;Cooling is provided, if necessary, to compensate for the heat generatedby the reaction. The reaction acn be terminated when up to one mol ofperacetic acid per'mol of u,/8-olefinic ester has been consumed, orbefore this point if desired. The reaction mixture then can be separatedinto its various components, such as, by fractional distillation torecover the selectively monoepoxidized product, i.e., vinyl or allylglycidic ester. 1 t

Theme of an inert organic medium is not a prerequisite in theepoxidation reaction, However, it has been observed that a faster andcleaner reaction is effected by employing the peracetic acid in an"inert organic medium such as ethyl acetate, acetone, and the like. A

solution comprising from about 10 to 50 weight percent of peraceticacid, based on the total weight of peracetic acid and inert organicmedium, is satisfactory; from .about20 to 40 weight percent of peraceticacid, based on the solution weight, is preferred.

The relative casein which the monoepoxidized products result from theinstant epoxidation reaction between peracetic acid.and an u,B-olefinicester as characterized by forrnula 1 supra is indeed surprising.According to terminal double bonds.

various "authorities and experts in the e ox field "suchas swem, supra,the epoxidation of an alpha,beta-olefinic ester, i.e., an ester whereina double bond is conjugated with a carbonyl group in the carboxylic acidportion of the ester molecule, with an epoxidizing" agent such asperbenzoic acid is effected with extreme difficulty, if at all. Thesuccessful epoxidation process afforded by the practice of the instantinvention is completely unpredictable on the basis'of informationavailable in the literature. The laborious and arduousroutes pursued byseveral skilled chemistsin the epoxy field to effect the introduction ofcxirane oxygen at the site of the alpha, beta double bond which is inconjugation with a carbdriyl gfoup is testimony lending totheunpre'dictability or the extreme diliiculty encountered by a directepoxication-cut i.e., a single-ste epoxidation process. The instantinvention, it is submitted, constitutes a definite and patentableadvance in the epoxy art.

The advantages of the instant process are readily apparent from thesingle-step nature of the operation. In addition, an economic source ofepoxide oxygen is utilized, i.e., per-acetic acid, rather than expensivehaloacetates and difficulty handled agents such as sodium amide or otherprohibitively expensive peroxygen chemicals such as perbenzoic acid orperoxytrifluoroacetic acid.

The vinyl and allyl glycidicesters prepared by the practice of thisinvention are a useful class of compounds. Thesecompounds arebifunctional by virtue of reactive epoxy and terminal ethylenic groupsand thus are useful as monomers which can be polymerized to form infusieble polymers; note U.S. Patent 2,680,109. They can be hydrolyzed toglycidic acids the utility of which is well recognized. Decarboxylation'ofthe resulting glycidic acids usually yield aldehydes or ketonesdepending upon whether the alpha substituent of said glycidic acid is ahydrogen or an alkyl" group. The vinyl and allyl glycidic esters of thisinvention also can be employed as stabilizers for chlorinated rubber.

The following examples are illustrative.

Example 1 substituted or conjugated double bonds were observed. Theabove-said fraction, ascertained to be allyl 2 -ethyl-2,3-epoxyhexanoate, had the following properties:

To 364 grams of allyl arethyl-p-propylacrylate (2 mols) were addeddropwise over a period of two hours 1490 grams of a 25.5 weight percentsolution of peracetic acid in ethyl acetate at a temperature of 50-60:C.

The temperature was maintained at 60 C. for a few '-hours, andsubsequently the reactionmixture was distilled under reducedpressureivith 700 grams of ethylbenzene to remove ethyl acetate and toazeotrope out the excess peracetic acid-and the acetic acid. After re-No bands characteristic of tri- 0 The distillate "was fractionated and a113 .gram fraction was recovered therefrom. This fraction- (28 percentyield) was subsequently determined to be allyl 2,3-epoxy-Z-ethylhexanoate. The above 113- gram fraction and a similar fraction(52 grams) prepared from a different run employing the sameingredientsin the-same manner were fractionated 84 C./1.5 mm. of Hg andhaving a refractive index (11 5 range of 1.4402-'-1.4407 were compositedand analyzed. The followingresults were obtained: Purity by HBr method"for epoxide.

analysis 100.2.percent. I Saponific'ation equivalent l 196 (calculated1% )1. Elemental Analysis: Found Calculated Carbon 66.76 66.6 Hydrogen9.12. 9.08

Infrared spectrum: Strong i'bands characteristic of terminal doublebonds. No bands characteristic of trisnbstituted or conjugated doublebonds.

To further chemically prove the structure of the aboveanalyzedfractions, 2 grams'of sodium metal was dissolved in grams ofZ-ethylhexanol. To this solution there were added 24.8 grams of theabove-analyzed fractions and 100 grams of dry benzene. The resultingmixture was heated under reflux on a still equipped with a fractionationcolumn. A mixture (40 milliliters) of benzene and allyl alcohol wasremoved slowly at the still head at a temperature of 77-78 C.(Reportedbinary azeotrope, boiling point 768 C., 17.4 percent allylalcohol.) Treatment of 10 milliliters of the distillate with onemilliliter of alpha-naphthyl isocyanate gave the alphanaphthyl urethanof allyl alcohol which after recrystallization from carbon tetrachloridemelted at 107.5"-

108 C. (Reported melting point 109 C.) The monoxide was identified asallyl 2-ethyl-2,3-epoxyhexanoate.

it is obvious that-various modifications of this invention can be madeby those skilled in the art without departing from the spirit and scopethereof.

What is claimed is:

1. An epoxidation process which comprises contacting an alpha,beta-olefinic ester having the formula:

wherein x is an integer less than two and including zero; and whereineach R is individually selected from the group consisting of hydrogen,alkyl, cyclopentyl, cyclohexyl, phenyl, tolyl, butylphenyl,benzyhphenethyl, and

.about'0. to about 100 C.

4. The process of claim 3 wherein the epoxidation reaction is conductedat a temperature in the range from about 25 to about 90 C.

5. The process for preparing vinyl polyalkyl-substituted glycidic esterwhich comprises contacting the corresponding alpha,beta-olefinic esterof vinyl alcohol, said moval of the ethylbenzene the crude reactionmixture was vacuumed distilled rapidly on a one-plate column.

alpha,beta-olefinic ester having at least two alkyl substitnentsattached to the alpha-beta-carboxylic acid residue thereof, withperacetic acid at a temperature in the range of from about 0 to aboutC., and for a period of time to consume up to one mole of 6. The processof claim 5 wherein said peracetic acid is employed as a solution in aninert organic medium.

7. The process of claim 6 wherein said inert organic medium is ethylacetate.

8. The process of claim 7 wherein said alpha,beta olefinic ester isvinyl a,fl-dialkylacrylate and said vinyl polyalkyl-substituted glycidicester is vinyl 2,3-dialkyl- 2,3-epoxypropionate.

9. The process of claim 8 wherein said vinyl 1x,B dialkylacrylate isvinyl 2-ethyl-3v-propylacrylate and said vinyl2,3-dialkyl-2,3-epoxypropiona'te is vinyl Z-ethyl- 2,3-epoxyhexanoate.

10. The process for preparing allyl polyalkyl-substituted glycidic esterwhich comprises contacting the corresponding alpha,beta-olefinic esterof allyl alcohol, said alpha, beta-olefinic ester having at least twoalkyl substituents "attached to the alpha,beta-carboxylic acid residuethereof, with peracetic acid, at a temperature in the range of fromabout 0 to about 100 C., and for a period of time to consume up to onemol of peracetic acid per mol of said alpha,beta-olefinic ester.

11. The process of claim 10 wherein said peracetic acid is employed as asolution in an inert organic medium. I

12; 'The process of claim 11 wherein said inert organic medium is ethylacetate.

13. The process of claim 12 wherein said alpha,betaolefinic'e'ster is'allyl mfi-dialkylacrylate and said allylpolyalkyl-substituted glycidicester' isaliyl 2,3-dialkyl- 2,3-epoxypropionat'ex' '14. 'The process ofclaim 13 wherein'said allyl 9M dialk'ylacrylate is allyl2-ethyl-3-propylacrylate and said v Y -Z poxypropionate' is' 'allyl2-fethyl-2,3- epoxyhexanoate.

References (Iited, in the file of this patent OTHER REFERENCES Swern;J.A.C.S., vol. 69', pp. 1692-1698 (1947). Elderfield: HeterocyclicCompounds, vol. 1, pp. (1950)

1. AN EPOXIDATION PROCESS WHICH COMPRISES CONTACTING AN ALPHA,BETA-OLEFINIC ESTER HAVING THE FORMULA: